This invention relates to switches of the kind including two terminals, a plurality of conductive tracks extending from each terminal, the conductive tracks connected with one terminal being electrically insulated from the tracks connected with the other terminal, the switch including a plurality of electrically-conductive bridging elements spaced from the tracks and displaceable between a first position where the bridging elements are spaced from the tracks and a second position where each bridging elements is in contact with a track connected with one terminal and a track connected with the other terminal such that current can flow in parallel between the two terminals via the conductive tracks and the bridging elements, and an actuator arranged to displace the bridging elements between the first and second position.
The switching of high currents is usually carried out by means of an electromagnetic relay or contactor employing a solenoid to displace an armature so that it bridges or isolates two contacts, thereby allowing or preventing current flow between the terminals. These relays can operate reliably but require relatively high currents to operate the solenoid. They are also bulky and heavy, and respond relatively slowly because of the mass of the armature. Lower currents can be switched using semiconductor devices such as FETs and thyristors but these have the disadvantage of introducing a voltage drop across the device and of not being suitable for higher current operation. U.S. Pat. No. 5,430,597 describes a current interrupting device of the above-specified kind having parallel branches extending from input and output lines, which are bridged by a number of micromechanical switches.